Vertical conduction Power MOSFET devices are well known. Such devices may be made as disclosed, for example, in U.S. Pat. No. 5,007,725, as planar, cellular devices, or can be made with a well known parallel stripe topology, or can be made using a trench technology.
The on-resistance (RDSON) of such devices is dependant in large measure on the resistivity of the epitaxially formed silicon layer which receives the device junctions, and this resistivity is, in turn, determined by the blocking voltage requirement of the final device. Thus, higher blocking voltages require a higher resistivity in the epitaxial layer, but this then causes an increase on resistance for the device.
It would be very desirable to provide a structure for high voltage devices, particularly those having a blocking voltage greater than about 100 volts, which can have a reduced on-resistance without sacrificing any substantial blocking voltage.